The invention relates to a method for operating an onboard power supply system of a motor vehicle, wherein the onboard power supply system has at least two electrical networks with different supply voltages, wherein a high-voltage network for supplying power to at least one low-voltage network supplies a specified amount of power to the at least one low-voltage network at a lower supply voltage compared to the supply voltage of the high-voltage network, wherein at least one network component, especially an electrical load, is connected to each onboard power supply system and the high-voltage network has at least one high-voltage battery connected to the high-voltage network.
Motor vehicles, especially electric motor vehicles having an electric drive, with an onboard power supply system having two or more parallel electric networks, are known, with the networks having different voltages. For example, a high-voltage network, to which for example a drive unit is connected, has a supply voltage of 72 V and a low-voltage network, to which electrical loads, such as different entertainment or information devices for the vehicle occupants or the like are connected, have an AC voltage of 12 V. Basically, the high-voltage network or the at least one low-voltage network supplies, especially also when the high-voltage battery of the high-voltage network is being charged, respective electrical loads with a certain amount of electrical power to operate the network components connected on the low-voltage network, or the amount of power supplied to the low-voltage network via the high-voltage network side also charges a low-voltage battery connected on the low-voltage network side.
In conventional methods for operating an onboard power supply system, a power shortfall or a power shortage may occur in the high-voltage network during charging of the high-voltage battery. This is caused, in particular, by the amount of power supplied to the low-voltage network and/or by the power consumption of the network components connected in the low-voltage network. Specifically, for example, the high-voltage battery in the high-voltage network may overheat while being charged, because a cooling unit cooling the high-voltage battery during the charging process may not receive sufficient electrical power.